.TH TTIMES91
.SH NAME:
ttimes91 \- travel time table access using tau-splines
.SH SYNOPSIS
.B ttimes91
.SH DESCRIPTION
ttimes91 is a simple user interface to access the travel times for
a wide variety of seismic phases at a given distance for specified
source depth, with user control over the selection of phases.
.LP
ttimes91 is set up to automatically access the tau-spline tables for 
the 1991 IASPEI Seismological Tables based on the velocity model 
iasp91 (direct access files - iasp91.hed, iasp91.tbl).
Other sets of tables can be accessed by invoking ttimes91 
with an argument e.g.
.br
ttimes91  iasp89
.br
for tables (iasp89.hed, iasp89.tbl).
.SS Phase specification
The phase specification scheme is briefly described when ttimes91
is run. Initially the specification procedure is set up in
query mode and responses need to be made at the star prompt (*),
a null response terminates the specification.  
The selection of phases can be done either by giving a sequence
of generic phase names or by specifying keywords. 
The available keywords are:
.nf
P      gives P-up, P, Pdiff, PKP and PKiKP
P+     gives P-up, P, Pdiff, PKP, PKiKP, PcP, pP, pPdiff, pPKP, 
             pPKiKP, sP, sPdiff, sPKP, sPKiKP 
S      gives S-up, S, Sdiff, SKS
S+     gives S-up, S, Sdiff, SKS, sS, SSdiff, sSKS,
             pS, pSdiff, pSKS
basic  gives P+, S+ and ScP, SKP, PKKP, SKKP, PP and PKPPKP
all    gives all available phases
.fi
.SS Depth specification
Once the choice of phase branches has been made the depth needs
to be specified and the specified tau-splines appropriate for 
that depth are then formed.
.SS Distance specification
The user is prompted for epicentral distance (delta) and the
travel time, slowness, curvature and depth derivative are displayed
for each phase.
.LP 
A new depth can be chosen by setting the distance negative, and
the procedure terminated but setting the depth negative as well.
.SH SEE ALSO
gtt91
.SH AUTHORS
R. Buland,
National Earthquake Information Centre, U.S. Geological Survey
Golden, Colorado
.br
B.L.N. Kennett,
Research School of Earth Sciences, Australian National University            
Canberra, Australia 
